BEC testing surprise.

[David Hall 9]

I have a small collection of BECs that were/are destined for use in my smaller F5J and sports gliders. I had found that the current output of the average ESC/BEC combo tends to be on the low side. For a 6 digital servo setup, I would choose something more like 4A min. For my latest 8 servo glider, a higher output is recommended in order to avoid supply collapse and brownout.

At the same time, I've started using opto ESCs, which can be remarkably small and light. I just need to find a separate BEC. I had a few small ones in hand and had bought a 4A and a 5A version for my plane.

As I recently bought a variable discharge load, I have all the kit I need to actually test my BECs, so I set up on my bench and ran all the BECs I had.

There were some surprises, but first let me say that QC, as always, plays a part in the performance we see.... you might see different performance.

I had set out a few tests for all the BECs, using a 3S battery.

First to see at what current the output collapsed (increasing quickly). Second, measure the voltage at 67% then 100% of the rated output and see how fast they heated up.

My ZTW Beatles 30A ESC output collapsed at 3A/4.1v. It gave 5.1v off load, 4.1v at 2A and at 3A (constant) it melted the heatshrink covering quite quickly. Test aborted.

Turnigy 5A 8-26V input SBEC. 5.3v no load, O/P collapsed at 4.1A. At 67%/5.0v it was getting too hot quickly. Test aborted.

Hobbyking 4A no brand SBEC. Output collapsed at 3.5A.

To cut out more wordy detail, the KingKong and Hobbywing 3A SBEC (UBEC) did very well, both maintained an output over their rated 3A. The HW maintained 5.4-5.1v right up to 3.5A when the output shut off (collapsed) and was the coolest at 67% output. The King Kong didn't keep such a good regulation but managed a transient output of 4.3A.

The real surprise was the tiny FPV bluesky UBEC 5v. This sold as a 3A device. I tested two. The best had excellent regulation, 5.3v, down to 5.1v at shutoff at over 4A. Managed 5.2v @2A, 5.2v @3A (getting warm), Held 2A fairly well, just getting too hot to hold after ~1.5min.

So... my fav ESC (this example) output is lower than rated, but that might be max transient output, not constant. The higher output SBEC of 4A and 5A are poor, and the super cheapies were very good in this test.... just what kind of noise is output on the supply is something else, I guess.

My tests were based on my need, to supply rather high transient output current whilst maintaining a reasonable steady output.

I think that is shows how the spec can vary almost wildly and probably be effected by QA issues.

 

Edited By David Hall 9 on 28/04/2020 17:05:01

[Nigel R]

Thanks for sharing your results.

Does somewhat confirm that these things have to be carefully sized with respect to servo loads.

[David Hall 9]

When I came back to RC, I bought a bunch of no-name ESCs and a few Chinese DSMX compatible receivers. They all looked fine. I set them up on the bench and added servos. When I got to three servos, one twitch on the stick set off a shutdown that cycled on and off. Two of the three Rx's did this. A good Rx was fine. Now I test more often.

But my test does show that my current supply need is probably lower than I thought. I use the ZTW ESC in several planes and have no problems. If the one tested is a representative sample (low shut-off current), then I use less than I thought I needed.

[David Hall 9]

As if to underline the effect of QA, I've just found another Hobbywing 3A UBEC, of the same type as the one that I tested. It's like a different device, the voltage regulation is much poorer than the first... it's a game of chance at the budget end ..

[Andy Stephenson]

I don't think it's anything to do with QA. these manufacturers know exactly how much their are over rating their specs. They are hoping the hobby user doesn't have the tech knowledge to prove they are lying.

I had a 40A ESC that burned out at 39.5A when one of the FETs popped. I sent it back to the supplier for inspection and they said you really need a 60A ESC if you are going to try and run it at 40A.

A.

[Nigel R]

There is a comic side to it, but at the end of the day, it is tacit admission that our gear is not as advertised. Some is badly designed, some badly advertised.